Optimisation of spray drying by response surface methodology for the production of Sinorhizobium meliloti powder formulation by using starch industry wastewater

A spray-drying process was optimised by response surface methodology for the development of a powder formulation of Sinorhizobium meliloti (produced in starch industry wastewater). The process parameters comprised drying temperature, air drying rate, spray pressure and feed sample rate. Cheese whey powder, sorbitol and sucrose were added at 10, 1 and 1% w/v, respectively before drying. Responses studied comprised cell viability, moisture and outlet temperature. Under the optimal conditions (maximum desirability = 0.81), the formulation showed cell viability of 6.8 × 109 CFU g−1, moisture of 11.4% and outlet temperature of 42 °C. During 4 months of refrigerated storage, viability was maintained at >109 CFU g−1. Analysis of inoculated alfalfa plants showed that powder formulation induced similar shoot yield on dry basis (144.6 mg) (p = 0.23) and nodulation index (15.2) (p = 0.18) compared to fresh cells cultured in standard media (shoot yield and nodulation index were 131 and 14 mg, respectively). Micrographs showed that cells were embedded in the mixture of additives (whey–sucrose–sorbitol) which acted as a matrix.